Sealing structure for compressors

ABSTRACT

A sealing structure for the shaft of a compressor. The sealing apparatus includes an inner ring, and outer ring, and a support ring. The inner ring and the outer rings have flexible annular lips that contact the surface of the rotary shaft. The support ring supports the inner lip and determines the position of the inner lip. The first lip permits fluid leakage along the surface of the shaft, while the second lip forms a fluid-tight seal with the shaft. The support ring prevents the internal pressure of the compressor from pressing the first lip against the shaft with excessive force, which extends the life of the sealing apparatus.

BACKGROUND OF THE INVENTION

The present invention relates to compressors that perform compression byrotating a rotary shaft with the power of an external drive source, andmore particularly, to a sealing structure that seals about the rotaryshaft to prevent fluids such as refrigerant and lubricating oil in thecompressor interior, or high pressure zone, from leaking out to thecompressor exterior, or low pressure zone.

Japanese Unexamined Patent Publication No. 6-300142 discloses an exampleof a sealing apparatus incorporated in a compressor to seal about arotary shaft of the compressor. As shown in FIG. 7, the sealingapparatus is provided with a rubber first lip ring 91 and a secondfluororesin second lip ring 2, which is arranged toward the outer sideof the compressor with respect to the first lip ring 91. The first lipring 91 and the second lip ring 92 respectively have lip portions 911,921 that contact the outer surface 931 of a rotary shaft 93 to preventleakage of fluid when the rotary shaft 93 is rotated or stopped.

The lip portion 911 of the first lip ring 91 permits leakage of fluidtoward the second lip ring 92 during rotation of the rotary shaft 93.The fluid leaking from the lip portion 911 (mainly lubricating oil)lubricates the lip portions 911, 921 to prevent frictional deteriorationand thermal deterioration caused by high temperatures. This increasesthe durability of the lip portions 911, 921.

It is significant that the contacting posture of the lip portion 911with respect to the peripheral surface 931 of the rotary shaft 93 be setand maintained at an optimal state to prevent the leakage of fluid whenstopping the rotation of the rotary shaft 93 while permitting leakagewhen rotating the rotary shaft 93, as described above. In the sealingapparatus of the above publication, the second lip ring 92 is adhered tothe first lip ring 91. The contacting posture of the lip portion 911with respect to the peripheral surface 931 of the rotary shaft 93 ismaintained by the support of the second lip ring 92.

However, when the pressure in the compressor becomes high, the first lipring 91, which is urged by the force of the high pressure, presses thelip portion 921 against the rotary shaft 93 with excessive force. Thisraises the temperature of the lip portion 921 and the temperature aboutthe lip portion 921. As a result, the heated lip portion 921 affects therubber lip portion 911, which has inferior heat resistance in comparisonto fluororesin, and causes thermal deterioration.

Accordingly, it is an objective of the present invention to provide acompressor sealing structure that suppresses the deterioration of thelip portion of the first lip ring and that has superior durability.

SUMMARY OF THE INVENTION

In the sealing apparatus according to the present invention, a posturemaintaining member is arranged between a first lip ring and a second lipring to support a contacting posture of a lip portion of a first lipring with respect to the outer surface of the rotary shaft. In thismanner, the contacting posture of the lip portion of the first lip ringis maintained by an exclusive posture maintaining member. Accordingly,when the pressure in a crank chamber is high, the first lip ring isprevented from pressing a lip portion of the second lip ring against theouter surface of the rotary shaft with excessive force. As a result,excessive heating of the lip portion of the second lip ring isprevented. Thus, thermal deterioration that would be caused by theheating is prevented.

The contacting posture of the lip portion of the first lip ring withrespect to the outer surface of the rotary shaft is arranged so thatfluid does not leak toward the second lip ring during rotation of therotary shaft. Accordingly, the fluid leakage optimally lubricates thelip portions of the first lip ring and the second lip ring and preventsfrictional deterioration and thermal deterioration of the lip portion.

The lip portion of the first lip ring has a distal portion that includesan acute flare projecting in a radially inward direction. The lipportion of the first lip ring contacts the outer surface of the rotaryshaft along an annular region of the outer surface with a distal end ofthe flare. The contacting posture of the lip portion of the first lipring with respect to the outer surface of the rotary shaft is arrangedso that an angle of an inclined surface defining the inner side of theflare with respect to the outer surface of the rotary shaft is smallerthan an angle of an inclined surface defining the outer side of theflare with respect to the outer surface of the rotary shaft.Accordingly, the lip portion of the first lip ring is provided withsufficient sealing capability when the rotation of the rotary shaft isstopped and permits leakage of a large amount of fluid when the rotaryshaft is rotated. As a result, the lubrication of the first lip ring andthe second lip ring with the fluid leakage is satisfactory. Thiseffectively prevents frictional deterioration and thermal deteriorationof the lip portion.

Space is provided between the posture maintaining member and the lipportion of the second lip ring. Accordingly, when the pressure in thecrank chamber is high, the load acting on the first lip ring is receivedby the posture maintaining member and not transmitted to the lip portionof the second lip ring. As a result, heating of the lip portion of thesecond lip ring is suppressed.

A pump structure actuated by the rotation of the rotary shaft isprovided in a contact zone between the lip portion of the second lipring and the outer surface of the rotary shaft. The pump structureforces fluid in the contact zone between the lip portion of the secondlip ring and the outer surface of the rotary shaft toward the inside ofthe compressor. Accordingly, the sealing capability of the lip portionof the second lip ring is enhanced. As a result, the sealing capabilityof the entire sealing apparatus is not degraded despite the fact thatthe structure is such that fluid leaks from the lip portion of the firstlip ring during rotation of the rotary shaft.

The pump structure includes a pump groove defined in at least one of thelip portion of the second lip ring and the outer surface of the rotaryshaft. The pump groove is provided only in a section located toward theinside of the compressor in the contact zone between the lip portion ofthe second lip ring and the outer surface of the rotary shaft and not ina section located toward the outside of the compressor. That is, thepump groove is arranged so that it is not opened toward the outside ofthe compressor. Accordingly, the residual fluid in the pump groove doesnot flow out of the compressor when the rotation of the rotary shaft isstopped. As a result, the sealing capability of the sealing structurewhen the rotation of the rotary shaft is stopped is enhanced.

The pump groove extends spirally about the axis of the second lip ring.Accordingly, a spiral pump effect is produced between the pump grooveand the outer surface of the rotary shaft during rotation of the rotaryshaft.

The compressor includes a crank chamber and a cylinder bore thatfunction as the inside of the compressor. A cam plate accommodated inthe crank chamber is integrally rotatable with the rotary shaft and isinclinable. A piston is reciprocally accommodated in the cylinder bore.The pressure of the crank chamber is altered to change the differencebetween the pressure of the crank chamber and the pressure of thecylinder bore and vary the inclination of the cam plate to controldisplacement. Accordingly, the pressure of the crank chamber becomeshigh to minimize displacement. The advantages of the above sealingstructure are effectively obtained, especially when applied to acompressor that withstands such harsh conditions.

The compressor is provided with a refrigerant circulation impeding meansfor impeding the circulation of refrigerant in an external refrigerantcircuit in cooperation with a minimum inclination of the cam plate. Therotary shaft never stops rotating. The advantages of the above sealingstructure are effectively obtained, especially when applied to acompressor that withstands such harsh conditions.

The compressor includes a fluid circulation passage defined in theinside of the compressor extending through a discharge pressure zone,the crank chamber, a suction pressure zone, and the cylinder bore whenthe refrigerant circulation impeding means impedes refrigerantcirculation in the external refrigerant circuit. A passage constitutingthe circulation passage connects the crank chamber with the suctionpressure zone and has an opening located in the crank chamber at thevicinity of the first lip ring. Accordingly, the amount of fluid flowingin the vicinity of the first lip ring in the crank chamber becomes largeduring minimum inclination operation, which produces harsh conditionsfor the lip portion of the first lip ring. As a result, the amount offluid necessary for lubricating the lip portions of the first lip ringand the second lip ring leaks continuously. This positively lubricatesthe lip portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a clutchless type variabledisplacement compressor to which a first embodiment of a sealingapparatus according to the present invention is applied;

FIG. 2 is an enlarged partial cross-sectional view showing the vicinityof the sealing apparatus of FIG. 1;

FIG. 3 is a plan view of a front, or outer, side of a second lip ringbefore the insertion of a rotary shaft;

FIG. 4A is an enlarged cross-sectional diagram showing the flare of FIG.2;

FIG. 4B is an enlarged cross-sectional diagram showing the flare of asealing apparatus of a comparative example;

FIG. 4C is an enlarged cross-sectional diagram showing the flare of asealing apparatus of another comparative example;

FIG. 5 is a graph comparing the effects of the sealing apparatus of thepreferred embodiment with that of the sealing apparatus of JapaneseUnexamined Patent Publication No. 6-300142, where the vertical axisindicates the temperature of the lip portion of the first lip ring,while the horizontal axis indicates the rotating speed of the rotaryshaft;

FIG. 6 is an enlarged partial cross-sectional view showing a secondembodiment of a sealing apparatus according to the present invention;and

FIG. 7 is an enlarged partial cross-sectional view showing the sealingapparatus of Japanese Unexamined Patent Publication No. 6-300142.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment according to the present invention will now bedescribed with reference to FIG. 1 to FIG. 5.

As shown in FIG. 1, a front housing 11 is coupled to the front end of acylinder block 12. A rear housing 13 is fixed to the rear end of thecylinder block 12 with a valve body 14 arranged in between. A crankchamber 15 is defined in the front housing 11 and the cylinder block 12.A rotary shaft 16 is rotatably supported by the front housing 11 and thecylinder block 12 extending through the crank chamber 15. One end of therotary shaft 16 extends through the front wall of the front housing 11and projects outward.

A boss 45 projects from the front wall of the front housing 11 andsurrounds the projecting end of the rotary shaft 16. A pulley 17 isrotatably supported by an angular bearing 18 on the peripheral surfaceof the boss 45. The pulley 17 is connected to the end of the rotaryshaft 16 projecting from the front housing 11. A belt 19 engaged withthe peripheral portion of the pulley 17 directly connects the pulley 17with a vehicle engine 20, serving as an external drive force, withoutusing an electromagnetic clutch or the like, which is expensive andheavy and which produces shock when actuated or de-actuated.Accordingly, the rotary shaft 16 is always rotated when the engine 20 isrunning.

A sealing apparatus 21 that seals the rotary shaft 16 is arrangedbetween an outer surface 161 of the rotary shaft 16 at the projectingend and the inner surface 451 of the boss portion 45. The structure ofthe sealing apparatus 21 will be described in detail later.

A rotary support 22 is fixed to the rotary shaft 16 in the crank chamber15. A swash plate 23, serving as a cam plate, is supported in a mannerthat it is slidable and inclinable with respect to the direction of theaxis L of the rotary shaft 16. A hinge mechanism 24 is arranged betweenthe rotary support 22 and the swash plate 23. The hinge mechanism 24enables the swash plate 23 to incline with respect to the axis L of therotary shaft 16 while rotating integrally with the rotary shaft 16. Whenthe center portion of the swash plate 23 moves toward the cylinder block12, the inclination of the swash plate 23 decreases. An inclinationdecreasing spring 26 is arranged between the rotary support 22 and theswash plate 23. The inclination decreasing spring 26 urges the swashplate 23 in a direction that decreases the inclination. An inclinationrestricting projection 221 is defined in the rear surface of the rotarysupport 22 to restrict the maximum inclination of the swash plate 23when abutting the swash plate 23.

An accommodating bore 121 extends through the center of the cylinderblock 12. A cylindrical shutter 28, which constitutes a refrigerantcirculation impeding means, is slidably accommodated in theaccommodating bore 121. A suction passage opening spring 29 is arrangedbetween the end surface of the accommodating bore 121 and the shutter 28to urge the shutter 28 toward the swash plate 23.

The rear end of the rotary shaft 16 is inserted into the shutter 28. Aradial bearing 30 is arranged between the rear end of the rotary shaft16 and the inner surface of the shutter 28. The radial bearing 30 slidestogether with the shutter 28 in the direction of the axis L with respectto the rotary shaft 16.

A suction passage 131 extends through the center of the rear housing 13and the valve body 14. The suction passage 131 is connected with theaccommodating bore 121. A positioning surface 141 is defined about theoutlet of the suction passage 131 on the front surface of the valve body14. A shutting surface 281 is defined on the distal surface of theshutter 28. The shutting surface 281 contacts or moves away from thepositioning surface 141 in accordance with the movement of the shutter28. The abutment between the shutting surface 281 and the positioningsurface 141 seals the space in between and disconnects the suctionpassage 131 from the interior space of the accommodating bore 121.

A thrust bearing 35 is arranged between the swash plate 23 and theshutter 28 and slidably supported on the rotary shaft 16. The thrustbearing 35 is urged by the suction passage opening spring 29 so that itis always held between the swash plate 23 and the shutter 28.

During inclination of the swash plate 23 toward the shutter 28, theinclination of the swash plate 23 is transmitted to the shutter 28 bythe thrust bearing 35. Thus, the shutter 28 moves toward the positioningsurface 141 against the urging force of the suction passage openingspring 29. This abuts the shutting surface 281 of the shutter 28 againstthe positioning surface 141. With the shutting surface 281 against thepositioning surface 141, further inclination of the swash plate 23 isrestricted. In the restricted state, the swash plate 23 is arranged atthe minimum inclination, which is slightly greater than zero degrees (asmeasured from a plane normal to the axis L).

Cylinder bores 122 extend through the cylinder block 12. A single-headedpiston 36 is accommodated in each cylinder bore 122. Each piston 36 iscoupled to the peripheral portion of the swash plate 23 by shoes 37 toconvert the rotational movement of the swash plate 23 to forward andreverse reciprocation of the piston 36.

A suction chamber 38, which is in a suction pressure zone, and adischarge chamber 39, which is in a discharge pressure zone, are eachdefined in the rear housing 13. Suction ports 142, suction flaps 143 foropening and closing the suction ports 142, discharge ports 144, anddischarge flaps 145 for opening and closing the discharge ports 144 areeach defined in the valve body 14. The reciprocation of each piston 36draws refrigerant gas from the suction chamber 38 into the associatedcylinder bore 122 through the associated suction ports 142 and suctionflaps 143. The refrigerant gas in the cylinder bore 122 is compressed toa predetermined pressure by the reciprocating movement of the associatedpiston 36 and discharged into the discharge chamber 39 through theassociated discharge port 144 and discharge flap 145.

The suction chamber 38 is connected to the accommodating bore 121through an aperture 146. The abutment of the shutting surface 281 of theshutter 28 against the positioning surface 141 disconnects the aperture146 from the suction passage 131. A conduit 46 extends along the axis ofthe rotary shaft 16. An inlet 461 of the conduit 46 opens in the crankchamber 15 in the vicinity of the sealing apparatus 21. An outlet 462opens inside the shutter 28, which is in the suction pressure zone. Apressure releasing hole 282 extends through the wall of the shutter 28and communicates the interior of the shutter 28 with the interior of theaccommodating bore 121.

A pressurizing passage 48 connects the discharge chamber 39 with thecrank chamber 15. A displacement control valve 49 is arranged in thepressurizing passage 48.

In the compressor of the above structure, the suction passage 131,through which refrigerant gas is drawn, and a discharge port 75, fromwhich the refrigerant gas in the discharge chamber 39 is discharged, areconnected by an external refrigerant circuit 76. A condenser 77, anexpansion valve 78, and an evaporator 79 are provided in the externalrefrigerant circuit 76.

A temperature sensor 80 is arranged in the vicinity of the evaporator79. The temperature sensor 80 detects the temperature of the evaporator80 and sends detected temperature information to a control computer 81.The control valve 49 has a solenoid 491 that is actuated and de-actuatedby the computer 81 based on the detected temperature information fromthe temperature sensor 80. When an air conditioner switch 82 is turnedon, the computer 81 instructs the de-actuation of the solenoid 491 ofthe control valve 49 when the detected temperature becomes lower than apredetermined temperature. A temperature lower than the predeterminedtemperature indicates a state in which frost may form in the evaporator79. When the air conditioner switch 82 is turned off, the computer 81de-actuates the solenoid 491.

De-actuation of the solenoid 491 opens the pressurizing passage 48 andconnects the discharge chamber 39 with the crank chamber 15. Thiscommunicates the high pressure refrigerant gas in the discharge chamber39 with the crank chamber 15 through the pressurizing passage 48 andincreases the pressure in the crank chamber 15. The pressure increase inthe crank chamber 15 shifts the swash plate 23 toward the minimuminclination position.

When the shutting surface 281 of the shutter 28 abuts against thepositioning surface 141, the cross-sectional passage area of the suctionpassage 131 becomes zero and the flow of refrigerant gas from theexternal refrigerant circuit 76 to the suction chamber 38 is impeded.

Since the minimum inclination of the swash plate 23 is not zero degrees,discharge from the cylinder bores 122 to the discharge chamber 39 takesplace even when the swash plate inclination is minimum. The refrigerantgas in the suction chamber 38 is drawn into the cylinder bores 122 anddischarged into the discharge chamber 39. In other words, when the swashplate inclination is minimum, a circulation passage is formed in thecompressor extending through the discharge chamber 39, the pressurizingpassage 48, the crank chamber 15, the conduit 46, the pressure releasinghole 282, the suction chamber 38, and the cylinder bores 122. Fluidmoving together with the refrigerant gas (mainly lubricating oil) passesthrough the circulation passage to lubricate the interior of thecompressor. There is a difference in pressure between the dischargechamber 39, the crank chamber 15, and the suction chamber 38. Thepressure difference and the cross-sectional passage area of the pressurereleasing hole 282 holds the swash plate 23 at the minimum inclinationin a stable manner.

The actuation of the solenoid 491 closes the pressurizing passage 48 andthe pressure in the crank chamber 15 is released through the conduit 46and the pressure releasing hole 282. This decreases the pressure of thecrank chamber 15. The pressure decrease shifts the swash plate 23 fromthe minimum inclination to the maximum inclination.

The sealing apparatus 21 will now be described.

As shown in FIG. 2, a case 51 includes a large cylindrical portion 511and a small cylindrical portion 512. The case 51 is inserted into theboss 45. Movement of the case 51 toward the crank chamber 15 isrestricted by the abutment of the distal end of the small cylindricalportion 512 against a stepped wall surface 452 defined in the rearwardend of the boss 45. The movement of the case 51 toward the outside ofthe compressor is restricted by the abutment of the large cylindricalportion 511 against a snap ring 52 fitted into the inner surface 451 ofthe boss 45. An O-ring 53 is fitted onto the small cylindrical portion512 and is in contact with the inner surface 451 of the boss 45.

A first lip ring 54, which is made of a synthetic resin such asacrylonitrile-butadiene rubber, is held by a first holding piece 55. Asecond lip ring 56, which is made of a fluororesin such as PTFE(polytetrafluoroethylene), is arranged at the front, or outer, side ofthe first lip ring 54. A posture maintaining ring 61, or posturemaintaining member, is arranged between the first lip ring 54 and thesecond lip ring 56. A second holding piece 58 is arranged at the front,or outer, side of the second lip ring 56. These members 54-56, 58, 61are accommodated in the case 51. In the case 51, the first holding piece55 abuts against a stepped surface 513 connecting the large cylindricalportion 511 with the small cylindrical portion 512. The second holdingpiece 58 abuts against an end 514, which is bent radially inward, of thelarge cylindrical portion 511. Thus, the first lip ring 54, the secondlip ring 56, and the posture maintaining ring 61 are held between thefirst holding piece 55 and a second holding piece 58.

The first lip ring 54 has a peripheral sealing portion 541, which is incontact with the inner surface of the large cylindrical portion 511, anda lip portion 542, which is in contact with the outer surface 161 of therotary shaft 16. The lip portion 542 extends through the interior of thecase 51 toward the crank chamber 15. The distal end of the lip portion542 is inclined radially downward. An acute flare 59 has an inclinedsurface 591 at the distal part of the lip as shown in FIG. 2 and FIG.4A. The inner annular edge 593 of the flare 59 is in contact with theouter surface 161 of the rotary shaft 16 along an annular region.

FIG. 4A is an enlarged view of the vicinity of the flare 59 of FIG. 2.As shown in the drawing, the surface 591 defining the crank chamber sideof the flare 59 is inclined with respect to the outer surface 161 of therotary shaft 16 by a predetermined angle θ1. In the same manner, aninclined surface 592 defining the compressor exterior side of the flare59 is inclined with respect to the outer surface 161 of the rotary shaft16 by a predetermined angle θ2. The contacting posture of the lipportion 542 is arranged so that the angle θ1 between the inclinedsurface 591 and the outer surface 161 and the angle θ2 between theinclined surface 592 and the outer surface 161 satisfies therelationship of θ1<θ2. The lip portion 542 of the first lip ring 54seals effectively when rotation of the rotary shaft 16 is stopped butpermits leakage of fluid from the crank chamber 15 toward the second lipring 56 during rotation of the rotary shaft 16.

FIG. 4B shows a comparative example in which the contacting posture ofthe lip portion 542 with respect to the rotary shaft 16 satisfies therelationship of θ1=θ2. FIG. 4C shows a comparative example in which thecontacting posture of the lip portion 542 with respect to the rotaryshaft 16 satisfies the relationship of θ1>θ2. These comparative examplesdiffer from the preferred embodiment in that fluid leakage from thecrank chamber toward the second lip ring 56 is not permitted duringrotation of the rotary shaft 16.

The difference between the preferred embodiment and the comparativeexamples will now be described. As shown in FIGS. 4A, 4B, and 4C, theflare 59 elastically contacts the outer surface 161 of the rotary shaft16, with the vicinity of its inner annular edge 593 flattened. Theportion of the flare 59 contacting the outer surface 161 of the rotaryshaft 16 includes the inner annular edge 593 and has a certain sealingwidth (as measured in the axial direction of the shaft 16). Thedouble-dotted curved lines of FIGS. 4A, 4B, 4C show the forcedistribution of the contact pressure of the flare 59 applied to theouter surface 161. As apparent from the distribution, if the contactingposture of the lip portion 542 with respect to the rotary shaft 16satisfies the condition of θ1=θ2, the flare 59 is flattened so that thepeak of the contact pressure, or the inner annular edge 593, is locatedat the center of the sealing width (indicated by the vertical brokenline FIG. 4B) If the condition of θ1>θ2 is satisfied, the flare 59 isflattened with the inner annular edge 593 located at a position offsetfrom the center (indicated by the vertical broken line in FIG. 4C)toward the crank chamber 15. If the condition of θ1<θ2 is satisfied, theflare 59 is flattened with its inner annular edge 593 located at aposition offset from the center toward the pulley 17. In other words, itcan be presumed that the sealing capability of the affected greatly byhow the flare 59 is flattened.

FIG. 3 shows the second lip ring 56 before insertion of the rotary shaft16. In this state, the second lip ring 56 is flat. As shown in FIG. 2,when the rotary shaft 16 is inserted, the inner portion of the secondlip ring 56 is bent toward the crank chamber 15. The bent portiondefines a lip portion 60. The lip portion 60 includes a seal surface 601having a predetermined width (as measured in the axial direction of theshaft 16). The seal surface 601 contacts the outer surface 161 of therotary shaft 16 along an annular region. Most of the lip portion 60 isincluded in the space between the lip portion 542 of the first lip ring54 and the outer surface 161 of the rotary shaft 16. The overlapping ofthe lip portion 542 of the first lip ring 54 and the lip portion 60 ofthe second lip ring 56 reduces the size of the sealing apparatus 21 inthe direction of the axis L.

A pump groove 602 extends spirally about the axis (L) of the second lipring 56 in the seal surface 601 of the lip portion 60. Accordingly, aspiral pump structure actuated by the rotation of the rotary shaft 16 isdefined by the pump groove 602 and the opposing outer surface 161 of therotary shaft 16. The pump groove 602 is provided only at the crankchamber end of the seal surface 601 and not the compressor exterior endof the seal surface 601. That is, the groove 602 is not formed in thefront end (the end nearest to the pulley 17) of the seal surface 601

The posture maintaining ring 61 has a peripheral portion 611 heldbetween the first lip ring 54 and the second lip ring 56. The posturemaintaining ring 61 also has an inner portion 612 that is bent to extendtoward the crank chamber 15 to separate the lip portion 542 of the firstlip ring 54 from the lip portion 60 of the second lip ring 56. A posturemaintaining portion 613, which is curved radially inward, is defined atthe distal or rearward portion of the inner portion 612. The posturemaintaining portion 613 contacts the lip portion 542 of the first lipring 54 to support the lip portion 542 from the side of the compressorexterior. The curved posture maintaining portion 613 enableslow-pressure contact with the lip portion 542. As apparent from thedrawing, a space is provided between the inner portion 612 of theposture maintaining ring 61 and the lip portion 60 of the second lipring 56.

The operation of the sealing apparatus 21 will now be described.

When the engine 20 is stopped and the rotation of the rotary shaft 16 isstopped, the elasticity of the lip portion 542 of the first lip ring 54causes the lip portion 542 to contact the outer surface 161 of therotary shaft 16. Accordingly, the leakage of fluid (refrigerant orlubricating oil) from the crank chamber 15, which is inside thecompressor, toward the exterior of the compressor is prevented.

However, as described above, the lip portion 542 of the first lip ring54 is arranged so that it enables leakage of fluid toward the second lipring 56 during rotation of the rotary shaft 16. Accordingly, when theengine 20 is started and the rotary shaft 16 is rotated, some fluid inthe crank chamber 15 leaks from the lip portion 542 toward the secondlip ring 56. However, the lip portion 60 of the second lip ring 56 sealsin the fluid that leaks from the lip portion 542 and prevents the fluidfrom leaking out of the compressor. Relative rotation between the groove602 and the outer surface 161 produces a pumping effect and positivelyreturns the fluid to the crank chamber 15 through the pump groove 602.This enhances the sealing capability of the lip portion 60.

During rotation of the rotary shaft 16, the leakage of fluid from thelip portion 542 of the first lip ring 54 enables fluid (mainlylubricating oil) to lubricate the lip portion 542 of the first lip ring54 and the lip portion 60 of the second lip ring 56. This preventsfrictional deterioration and thermal deterioration of the lip portions542, 60.

The following advantages are obtained from the structure of thepreferred embodiment.

(1) During minimum inclination operation of the compressor, the highpressure refrigerant gas in the discharge chamber 39 may increase thepressure of the crank chamber 15 to, for example, about 7 kgf/cm²(gauge). The high pressure of the crank chamber 15 tends to deform thefirst lip ring 54. However, the lip portion 542 of the first lip ring 54is supported by the posture maintaining portion 613 of the posturemaintaining ring 61. This prevents deformation of the first lip ring 54.Therefore, the first lip ring 54 does not press the lip portion 60 ofthe second lip ring 56 against the outer surface 161 of the rotary shaft16 with excessive force. As a result, excessive heating of the lipportion is avoided. This prevents heating of the lip portion 60, whichis made of a synthetic rubber, which has a heat resistance that isinferior to fluororesin, and improves the durability of the sealingapparatus 21.

(2) The contacting posture of the lip portion 542 with respect to therotary shaft 16 is arranged so that the angle θ1 between the inclinedsurface 591 and the outer surface 161 and the angle θ2 between theinclined surface 592 and the peripheral surface 161 satisfies therelationship of θ1<θ2. Accordingly, the lip portion 542 sealseffectively when the rotation of the rotary shaft 16 is stopped whilepreventing a large amount of fluid leakage during rotation of the rotaryshaft 16. This results in satisfactory lubrication of the lip portion542 of the first lip ring 54. Thus, as marked by the squares in FIG. 5,the heating of the lip portion 542 is reduced in comparison with thesealing apparatus of Japanese Unexamined Patent Publication No. 6-300142(marked by circles) under the same conditions.

(3) The pump groove 602 is defined in the lip portion 60 of the secondlip ring 56. A spiral pumping effect is produced by the pump groove 602and the outer surface 161 during rotation of the rotary shaft 16.Accordingly, the sealing performance of the lip portion 60 of the secondlip ring 56 is improved. The improvement of the sealing performance ofthe lip portion 60 during rotation of the rotary shaft 16 preventsdegradation of the sealing performance of the entire sealing apparatus21, even if leakage of fluid from the lip portion 542 of the first lipring 54 is permitted.

(4) The pump groove 602 is provided only at the crank chamber side ofthe seal surface 601 of the lip portion 60 and not the compressorexterior side of the seal surface 601. In other words, the pump groove602 does not open toward the exterior of the compressor. Accordingly, incases such as when the rotation of the rotary shaft 16 is stopped, theresidual fluid in the pump groove 602 does not flow out of thecompressor. This improves the sealing performance of the sealingapparatus 21 when the rotation of the rotary shaft 16 is stopped.

(5) The compressor of the preferred embodiment is a variabledisplacement compressor. Thus, displacement is varied by adjusting thepressure of the crank chamber 15. Accordingly, the pressure in the crankchamber 15 becomes high during minimum inclination operation. Theadvantages of the above sealing structure 21 are especially effectivewhen applied to a variable displacement compressor that withstands suchharsh conditions.

(6) Further to the above advantage (5), the compressor of the preferredembodiment is a clutchless compressor and the rotary shaft 16 is alwaysrotated when the engine 20 is running. That is, the lip portion 542 ofthe first lip ring 54 always slides along the outer surface 161 of therotary shaft 16 when the engine 20 is running. As described above, thepressure of the crank chamber 15 is high during minimum displacementoperation. In addition, minimum displacement operation may be continuedfor a long period of time during the winter. The advantages of the abovesealing structure 21 are especially effective when applied to a variabledisplacement compressor that withstands such harsh conditions.

(7) The inlet 461 of the conduit 46, which constitutes an internalcirculation passage for fluid during minimum displacement operation, islocated in the vicinity of the first lip ring 54 of the sealingapparatus 21. Accordingly, during minimum inclination operation, whichproduces a harsh environment for the sealing apparatus 21, there is anincrease in the amount of fluid flowing in the vicinity of the first lipring 54 in the crank chamber 15. As a result, the required amount offluid necessary for lubricating the lip portion 542 leaks continuously.This further reduces heating of the lip portion 60.

Second Embodiment

FIG. 6 shows a second embodiment. In addition to the main sealingstructure of the sealing apparatus 21 of the first embodiment, a sealingapparatus 71 of this embodiment includes a fluororesin third lip ring72, the structure of which is similar to the second lip ring 56. Thethird lip ring 72 is arranged at the outer side of the second lip ring56 and has a lip portion 721 that contacts the outer surface 161 of therotary shaft 16. The lip portion 721 is not provided with the pumpgroove 602.

The following advantages are obtained from the structure of thisembodiment.

(1) The sealing apparatus 71 has the third lip ring 72. Accordingly, ifthe second lip ring 56 deteriorates, the lip portion 721 of the thirdlip ring 72 functions as a further seal and prevents the fluid in thecrank chamber 15 from leaking out of the compressor. This furtherimproves the durability of the sealing apparatus 71.

(2) The lip portion 721 of the third lip ring 72 prevents dust or thelike from entering the compressor. Accordingly, the lip portion 60 ofthe second lip ring 56 is not exposed to dust. This improves the sealingperformance of the second lip ring 56 and enhances the sealingperformance of the sealing apparatus 71.

The present invention may be embodied as described below withoutdeparting from the spirit or scope of the invention.

(1) In the above embodiments, the contacting posture of the lip portion542 with respect to the rotary shaft 16 may be arranged as shown in FIG.4B or FIG. 4C. Even if arranged in such manner, the supporting functionof the posture maintaining ring 61 prevents the first lip ring 54 frompressing the lip portion 60 of the second lip ring 56 against the rotaryshaft 16 while permitting a small amount of fluid to flow toward thesecond lip ring 56 during rotation of the rotary shaft 16. Thus, asmarked by the triangles in FIG. 5, the heating of the lip portion 542 ofthe lip ring 56 is positively reduced in comparison with the sealingapparatus of Japanese Unexamined Patent Publication No. 6-300142 (markedby circles).

(2) In the above embodiments, the contacting posture of the lip portion542 with respect to the rotary shaft 16 may be arranged so that fluiddoes not leak even when the rotary shaft 16 is rotating.

(3) The present embodiment may be applied to the sealing structure of acompressor employing a clutch.

What is claimed is:
 1. A seal apparatus for a rotary shaft of acompressor, wherein the seal apparatus seals about the rotary shaftbetween a high pressure inner zone and a low pressure outer zone, andwherein fluid lubricant is located in the high pressure zone, theapparatus comprising:a first flexible ring having a first lip portionfor contacting the surface of the rotary shaft, wherein the first ringhas a low pressure side, which is exposed to a relatively low pressure,and a high pressure side, which is exposed to the high pressure zone; asecond flexible ring located on the low pressure side of the first lipportion, wherein the second ring has a second lip portion that contactsthe surface of the rotary shaft; and a support ring located between thefirst ring and the second ring, wherein the support ring supports thefirst lip and determines the position of the first lip with respect tothe shaft.
 2. The seal apparatus according to claim 1, wherein the firstlip has an inner inclined surface extending from the surface of theshaft toward the high pressure zone and an outer inclined surfaceextending from the surface of the shaft toward the low pressure zone,wherein the angle between the surface of the shaft and the innerinclined surface is less than the angle between the outer inclinedsurface and the surface of the shaft, and wherein the structure andarrangement of the first lip permits leakage of fluid from the highpressure zone to the low pressure side of the first lip.
 3. The sealapparatus according to claim 1, wherein the second lip is located withinthe support ring, and an annular space is formed between the second lipand the support ring.
 4. The seal apparatus according to claim 1,wherein a pump structure is defined by the second lip and the surface ofthe shaft for forcing fluid lubricant from between the surface of theshaft and the second lip towards the first lip.
 5. The seal apparatusaccording to claim 4, wherein the pump structure includes a spiralgroove formed in one of the second lip and the surface of the shaft, andwherein the spiral groove is sealed from the low pressure zone by anannular portion of the second lip.
 6. The seal apparatus according toclaim 1, wherein the compressor includes:a crank chamber; a cam plate,which is inclinable with respect to the rotary shaft and which rotatesintegrally with the rotary shaft; a cylinder bore; and a piston locatedwithin the cylinder bore, wherein the piston is connected to the camplate, and wherein the pressure in the crank chamber is varied tocontrol the inclination of the cam plate and the displacement of thecompressor.
 7. The sealing apparatus according to claim 6, wherein arefrigeration circuit is attached to the compressor, and a power sourceis coupled to the rotary shaft with a clutchless transmission apparatussuch that the compressor operates continuously when the power sourceoperates.
 8. The sealing apparatus according to claim 6, wherein thecompressor includes a suction chamber and an internal passage forconducting fluid from the crank chamber toward a suction chamber, andwherein the internal passage has an inlet located in close proximity tothe first lip.
 9. The sealing apparatus according to claim 1, whereinthe second ring is made of flouroresin.
 10. A seal apparatus for arotary shaft of a compressor, wherein the seal apparatus seals about therotary shaft between a high pressure inner zone and a low pressure outerzone, and wherein fluid lubricant is located in the high pressure zone,the apparatus comprising:a first flexible ring having a first lipportion for contacting the surface of the rotary shaft, wherein thefirst ring has a low pressure side, which is exposed to a relatively lowpressure and a high pressure side, which is exposed to the high pressurezone, wherein the first ring is constructed and arranged to permitleakage of fluid lubricant from the high pressure zone to the lowpressure side; a second flexible ring located on the low pressure sideof the first lip portion, wherein the second ring has a second lipportion that contacts the surface of the rotary shaft and wherein thesecond ring has a generally radially extending portion and an axiallyextending portion joined to the radially extending portion, wherein theaxially extending portion forms the second lip; and a support ringlocated between the first ring and the second ring, wherein the supportring supports the first lip and fixes the position of the first lip withrespect to the shaft.
 11. The sealing apparatus according to claim 10,wherein the second ring is made of flouroresin.
 12. The seal apparatusaccording to claim 10, wherein the first lip has an inner inclinedsurface extending from the surface of the shaft towards the highpressure zone and an outer inclined surface extending from the surfaceof the shaft towards the low pressure zone, wherein the angle betweenthe surface of the shaft and the inner inclined surface is less than theangle between the outer inclined surface and the surface of the shaft.13. The seal apparatus according to claim 12, wherein the second lip islocated within the support ring, and an annular space is formed betweenthe second lip and the support ring.
 14. The seal apparatus according toclaim 13, wherein a pump structure is defined by the second lip and thesurface of the shaft for forcing fluid lubricant from between thesurface of the shaft and the second lip towards the first lip.
 15. Theseal apparatus according to claim 14, wherein the pump structureincludes a spiral groove formed in one of the second lip and the surfaceof the shaft, and wherein the spiral groove is sealed from the lowpressure zone by an annular portion of the second lip.
 16. A compressorhaving a seal apparatus, wherein the compressor includes:a housing; acrank chamber within the housing, wherein the interior of the crankchamber is a high pressure zone containing fluid lubricant; a rotaryshaft extending from the outside of the compressor to the crank chamber;a cam plate, which is inclinable with respect to the rotary shaft andwhich rotates integrally with the rotary shaft; a cylinder bore; apiston located within the cylinder bore, wherein the piston is connectedto the cam plate, and wherein the pressure in the crank chamber isvaried to control the inclination of the cam plate and the displacementof the compressor, wherein the seal apparatus comprises:a first flexiblering attached to the housing, the first flexible ring having a first lipportion for contacting the surface of the rotary shaft, wherein thefirst lip portion extends axially toward the crank chamber, and whereinthe first ring has a low pressure side, which is exposed to a relativelylow pressure, and a high pressure side, which is exposed to the highpressure zone; a second flexible ring located on the low pressure sideof the first lip portion, wherein the second ring is attached to thehousing and has a second lip portion that contacts the surface of therotary shaft, and wherein the second lip portion extends axially towardthe crank chamber; and a support ring located between the first ring andthe second ring, wherein the support ring supports the first lip andfixes the position of the first lip with respect to the shaft, whereinthe support ring has a portion that extends axially toward the crankchamber.
 17. The compressor according to claim 16, wherein the first liphas an inner inclined surface extending from the surface of the shafttowards the high pressure zone and an outer inclined surface extendingfrom the surface of the shaft towards the low pressure zone, wherein theangle between the surface of the shaft and the inner inclined surface isless than the angle between the outer inclined surface and the surfaceof the shaft.
 18. The compressor according to claim 16, wherein thesecond lip is located within the support ring, and an annular space isformed between the second lip and the support ring.
 19. The compressoraccording to claim 16, wherein a pump structure is defined by the secondlip and the surface of the shaft for forcing fluid lubricant frombetween the surface of the shaft and the second lip towards the firstlip.
 20. The compressor according to claim 19, wherein the pumpstructure includes a spiral groove formed in one of the second lip andthe surface of the shaft, and wherein the spiral groove is sealed fromthe low pressure zone by an annular portion of the second lip.
 21. Thecompressor according to claim 16, wherein a refrigeration circuit isattached to the compressor, and a power source is coupled to the rotaryshaft with a clutchless transmission apparatus such that the compressoroperates continuously when the power source operates.
 22. The compressoraccording to claim 16, wherein the compressor includes a suction chamberand an internal passage for conducting fluid from the crank chambertoward a suction chamber, and wherein the internal passage has an inletlocated in close proximity to the first lip portion.